Effect of a common missense variant in LIPA gene on fatty liver disease and lipid phenotype: New perspectives from a single-center observational study.

Lysosomal acid lipase deficiency (LAL-D) is an autosomal recessive disease characterized by hypoalphalipoproteinemia, mixed hyperlipemia, and fatty liver (FL) due to mutations in LIPAse A, lysosomal acid type (LIPA) gene. The rs1051338 single-nucleotide polymorphism (SNP) in LIPA gene, in vitro, could adversely affect the LAL activity (LAL-A). Nonalcoholic fatty liver disease (NAFLD) is often associated with metabolic syndrome, and the diagnosis requires the exclusion of excess of alcohol intake and other causes of hepatic disease. The aim of the study was to evaluate the impact of rs1051338 rare allele on lipid phenotype, severity of FL, and LAL-A in patients suffering from dyslipidemia associated with NAFLD. We selected 74 subjects with hypoalphalipoproteinemia or mixed hyperlipemia and evaluated transaminases, liver assessment with controlled attenuation parameter (CAP), LAL-A, rs1051338 SNP genotype. The presence of rare allele caused higher levels of triglycerides and hepatic transaminase and lower levels of high-density lipoprotein cholesterol (HDL-C). Multivariate analysis highlighted independent association between rare allele and FL severity in subjects with NAFLD. The rs1051338 SNP may modulate FL severity and atherogenic dyslipidemia in patients suffering from NAFLD.

Identification and functional analysis of missense mutations in the lecithin cholesterol acyltransferase gene in a Chilean patient with hypoalphalipoproteinemia.

BACKGROUND: Lecithin-cholesterol acyltransferase (LCAT) is a plasma enzyme that esterifies cholesterol in high- and low-density lipoproteins (HDL and LDL). Mutations in LCAT gene causes familial LCAT deficiency, which is characterized by very low plasma HDL-cholesterol levels (Hypoalphalipoproteinemia), corneal opacity and anemia, among other lipid-related traits. Our aim is to evaluate clinical/biochemical features of a Chilean family with a proband showing clinical signs of familial LCAT deficiency, as well as to identify and assess the functional effects of LCAT mutations. METHODS: An adult female proband with hypoalphalipoproteinemia, corneal opacity and mild anemia, as well as her first-degree relatives, were recruited for clinical, biochemical, genetic, in-silico and in-vitro LCAT analysis. Sequencing of exons and intron-exon boundaries was performed to identify mutations. Site-directed mutagenesis was carried out to generate plasmids containing cDNA with wild type or mutant sequences. Such expression vectors were transfected to HEK-239 T cells to asses the effect of LCAT variants in expression, synthesis, secretion and enzyme activity. In-silico prediction analysis and molecular modeling was also used to evaluate the effect of LCAT variants. RESULTS: LCAT sequencing identified rare p.V333 M and p.M404 V missense mutations in compound heterozygous state in the proband, as well the common synonymous p.L363 L variant. LCAT protein was detected in proband's plasma, but with undetectable enzyme activity compared to control relatives. HEK-293 T transfected cells with vector expression plasmids containing either p.M404 V or p.V333 M cDNA showed detectable LCAT protein expression both in supernatants and lysates from cultured cells, but with much lower enzyme activity compared to cells transfected with the wild-type sequence. Bioinformatic analyses also supported a causal role of such rare variations in LCAT lack of function. Additionally, the proband carried the minor allele of the synonymous p.L363 L variant. However, this variant is unlikely to affect the clinical phenotype of the proband given its relatively high frequency in the Chilean population (4%) and its small putative effect on plasma HDL-cholesterol levels. CONCLUSION: Genetic, biochemical, in vitro and in silico analyses indicate that the rare mutations p.M404 V and p.V333 M in LCAT gene lead to suppression of LCAT enzyme activity and cause clinical features of familial LCAT deficiency.

A novel splicing mutation in the ABCA1 gene, causing Tangier disease and familial HDL deficiency in a large family.

Tangier disease is a rare disorder of lipoprotein metabolism that presents with extremely low levels of HDL cholesterol and apoprotein A-I. It is caused by mutations in the ATP-binding cassette transporter A1 (ABCA1) gene. Clinical heterogeneity and mutational pattern of Tangier disease are poorly characterized. Moreover, also familial HDL deficiency may be caused by mutations in ABCA1 gene. ATP-binding cassette transporter A1 (ABCA1) gene mutations in a patient with Tangier disease, who presented an uncommon clinical history, and in his family were found and characterized. He was found to be compound heterozygous for two intronic mutations of ABCA1 gene, causing abnormal pre-mRNAs splicing. The novel c.1510-1G > A mutation was located in intron 12 and caused the activation of a cryptic splice site in exon 13, which determined the loss of 22 amino acids of exon 13 with the introduction of a premature stop codon. Five heterozygous carriers of this mutation were also found in proband's family, all presenting reduced HDL cholesterol and ApoAI (0.86 ±â€¯0.16 mmol/L and 92.2 ±â€¯10.9 mg/dL respectively), but not the typical features of Tangier disease, a phenotype compatible with the diagnosis of familial HDL deficiency. The other known mutation c.1195-27G > A was confirmed to cause aberrant retention of 25 nucleotides of intron 10 leading to the insertion of a stop codon after 20 amino acids of exon 11. Heterozygous carriers of this mutation also showed the clinical phenotype of familial HDL deficiency. Our study extends the catalog of pathogenic intronic mutations affecting ABCA1 pre-mRNA splicing. In a large family, a clear demonstration that the same mutations may cause Tangier disease (if in compound heterozygosis) or familial HDL deficiency (if in heterozygosis) is provided.

Genetic and secondary causes of severe HDL deficiency and cardiovascular disease.

We assessed secondary and genetic causes of severe HDL deficiency in 258,252 subjects, of whom 370 men (0.33%) and 144 women (0.099%) had HDL cholesterol levels <20 mg/dl. We excluded 206 subjects (40.1%) with significant elevations of triglycerides, C-reactive protein, glycosylated hemoglobin, myeloperoxidase, or liver enzymes and men receiving testosterone. We sequenced 23 lipid-related genes in 201 (65.3%) of 308 eligible subjects. Mutations (23 novel) and selected variants were found at the following gene loci: 1) ABCA1 (26.9%): 2 homozygotes, 7 compound or double heterozygotes, 30 heterozygotes, and 2 homozygotes and 13 heterozygotes with variants rs9282541/p.R230C or rs111292742/c.-279C>G; 2) LCAT (12.4%): 1 homozygote, 3 compound heterozygotes, 13 heterozygotes, and 8 heterozygotes with variant rs4986970/p.S232T; 3) APOA1 (5.0%): 1 homozygote and 9 heterozygotes; and 4) LPL (4.5%): 1 heterozygote and 8 heterozygotes with variant rs268/p.N318S. In addition, 4.5% had other mutations, and 46.8% had no mutations. Atherosclerotic cardiovascular disease (ASCVD) prevalence rates in the ABCA1, LCAT, APOA1, LPL, and mutation-negative groups were 37.0%, 4.0%, 40.0%, 11.1%, and 6.4%, respectively. Severe HDL deficiency is uncommon, with 40.1% having secondary causes and 48.8% of the subjects sequenced having ABCA1, LCAT, APOA1, or LPL mutations or variants, with the highest ASCVD prevalence rates being observed in the ABCA1 and APOA1 groups.

Hypoalphalipoproteinemia and BRAFV600E Mutation Are Major Predictors of Aortic Infiltration in the Erdheim-Chester Disease.

Objective- Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis characterized by the infiltration of multiple tissues with lipid-laden histiocytes. Cardiovascular involvement is frequent in ECD and leads to a severe prognosis. The objective of this study was to determine whether an alteration of lipid metabolism participates in the lipid accumulation in histiocytes and the cardiovascular involvement in ECD. Approach and Results- An analysis of plasma lipid levels indicated that male ECD patients carrying the BRAFV600E (B-Raf proto-oncogene, serine/threonine kinase) mutation exhibited hypoalphalipoproteinemia, as demonstrated by low plasma HDL-C (high-density lipoprotein cholesterol) levels. Capacity of sera from male BRAFV600E ECD patients to mediate free cholesterol efflux from human macrophages was reduced compared with control individuals. Cardiovascular involvement was detected in 84% of the ECD patients, and we reported that the presence of the BRAFV600E mutation and hypoalphalipoproteinemia is an independent determinant of aortic infiltration in ECD. Phenotyping of blood CD14+ cells, the precursors of histiocytes, enabled the identification of a specific inflammatory signature associated with aortic infiltration which was partially affected by the HDL phenotype. Finally, the treatment with vemurafenib, an inhibitor of the BRAFV600E mutation, restored the defective sera cholesterol efflux capacity and reduced the aortic infiltration. Conclusions- Our findings indicate that hypoalphalipoproteinemia in male ECD patients carrying the BRAFV600E mutation favors the formation of lipid-laden histiocytes. In addition, we identified the BRAF status and the HDL phenotype as independent determinants of the aortic involvement in ECD with a potential role of HDL in modulating the infiltration of blood CD14+ cells into the aorta.

Large-scale deletions of the ABCA1 gene in patients with hypoalphalipoproteinemia.

Copy-number variations (CNVs) have been studied in the context of familial hypercholesterolemia but have not yet been evaluated in patients with extreme levels of HDL cholesterol. We evaluated targeted, next-generation sequencing data from patients with very low levels of HDL cholesterol (i.e., hypoalphalipoproteinemia) with the VarSeq-CNV® caller algorithm to screen for CNVs that disrupted the ABCA1, LCAT, or APOA1 genes. In four individuals, we found three unique deletions in ABCA1: a heterozygous deletion of exon 4, a heterozygous deletion that spanned exons 8 to 31, and a heterozygous deletion of the entire ABCA1 gene. Breakpoints were identified with Sanger sequencing, and the full-gene deletion was confirmed by using exome sequencing and the Affymetrix CytoScan HD array. Previously, large-scale deletions in candidate HDL genes had not been associated with hypoalphalipoproteinemia; our findings indicate that CNVs in ABCA1 may be a previously unappreciated genetic determinant of low levels of HDL cholesterol. By coupling bioinformatic analyses with next-generation sequencing data, we can successfully assess the spectrum of genetic determinants of many dyslipidemias, including hypoalphalipoproteinemia.

Naturally Occurring Variants in LRP1 (Low-Density Lipoprotein Receptor-Related Protein 1) Affect HDL (High-Density Lipoprotein) Metabolism Through ABCA1 (ATP-Binding Cassette A1) and SR-B1 (Scavenger Receptor Class B Type 1) in Humans.

OBJECTIVE: Studies into the role of LRP1 (low-density lipoprotein receptor-related protein 1) in human lipid metabolism are scarce. Although it is known that a common variant in LRP1 (rs116133520) is significantly associated with HDL-C (high-density lipoprotein cholesterol), the mechanism underlying this observation is unclear. In this study, we set out to study the functional effects of 2 rare LRP1 variants identified in subjects with extremely low HDL-C levels. APPROACH AND RESULTS: In 2 subjects with HDL-C below the first percentile for age and sex and moderately elevated triglycerides, we identified 2 rare variants in LRP1: p.Val3244Ile and p.Glu3983Asp. Both variants decrease LRP1 expression and stability. We show in a series of translational experiments that these variants culminate in reduced trafficking of ABCA1 (ATP-binding cassette A1) to the cell membrane. This is accompanied by an increase in cell surface expression of SR-B1 (scavenger receptor class B type 1). Combined these effects may contribute to low HDL-C levels in our study subjects. Supporting these findings, we provide epidemiological evidence that rs116133520 is associated with apo (apolipoprotein) A1 but not with apoB levels. CONCLUSIONS: This study provides the first evidence that rare variants in LRP1 are associated with changes in human lipid metabolism. Specifically, this study shows that LRP1 may affect HDL metabolism by virtue of its effect on both ABCA1 and SR-B1.

Reduced platelet count, but no major platelet function abnormalities, are associated with loss-of-function ATP-binding cassette-1 gene mutations.

Loss-of-function mutations of the the ATP-binding cassette-1 (ABCA1) gene are the cause of Tangier disease (TD) in homozygous subjects and familial HDL deficiency (FHD) in heterozygous subjects. These disorders are characterized by reduced plasma HDL-cholesterol (HDL-C) and altered efflux of cholesterol from cells. Previous studies in TD patients and ABCA1-/- murine models reported defects in platelet count, morphology, and function, but the issue is still controversial. We analyzed three subjects with low to very low HDL-C levels due to the loss-of-function mutations of the ABCA1 gene. Two related patients with FHD were heterozygous carriers of two mutations on the same ABCA1 allele; one, with TD, was homozygous for a different mutation. Mild to moderate thrombocytopenia was observed in all the patients. No morphological platelet abnormalities were detected under optical or EM. History of moderate bleeding tendency was recorded only in one of the FHD patients. Only limited alterations in platelet aggregation and activation of the integrin αIIbß3 were observed in one FHD patient. While α-granule secretion (P-selectin), content, and secretion of platelet δ-granules (serotonin, ATP, and ADP) and thromboxane (TX) A2 synthesis were normal in all the patients, the expression of lysosomal CD63, in response to some agonists, was reduced in TD patients. In conclusion, three patients carrying ABCA1 genetic variants had low platelet count, with the lowest values observed in TD, not associated with major alterations in platelet morphology and response to agonists or bleeding.

Interactions of Six SNPs in ABCA1gene and Obesity in Low HDL-C Disease in Kazakh of China.

OBJECTIVE: To detect the interactions between six functional polymorphisms in ABCA1 and obesity in Kazakhs with low HDL-C levels. METHODS: A total of 204 patients with low HDL-C and 207 health control subjects, which were randomly selected from among 5692 adult Kazakhs, were matched for age and sex. We genotyped ABCA1 single nucleotide polymorphisms of rs2515602, rs3890182, rs2275542, rs2230806, rs1800976, and rs4149313. RESULTS: (1) The genotypic and allelic frequencies of rs2515602, rs2230806 and rs4149313 were different between normal HDL-C and low HDL-C subjects, the genotypic frequency of rs2275542 was also different between normal HDL-C and low HDL-C subjects (p < 0.05); (2) the level of HDL-C (rs2515602 and rs2275542) in normal HDL-C subjects were different among the genotypes (p < 0.05); the levels of TC, LDL-C (rs2515602, rs4149313); TG (rs2515602, rs1800976, rs4149313) in low HDL-C patients were different among the genotypes (p < 0.05); (3) interactions between the rs3890182, rs2275542, rs180096, and rs4149313 polymorphisms in ABCA1 gene and obesity may be associated with low HDL-C disease; (4) the C-C-C-A-A-G, T-C-C-A-A-A, T-C-C-A-A-G, C-C-C-A-A-A, C-T-G-G-A-A, and T-T-C-G-A-A haplotypes were significant between the subjects with normal HDL-C and low HDL-C level (p < 0.05). CONCLUSIONS: The differences in serum lipid levels between normal HDL-C and low HDL-C subjects among Kazakhs might partly result from ABCA1 gene polymorphisms; ABCA1 gene polymorphisms may be associated with low HDL-C disease; the low HDL-C disease might partly result from interactions between ABCA1 gene polymorphisms and obesity; the C-C-C-A-A-G, T-C-C-A-A-A, and T-C-C-A-A-G haplotypes may serve as risk factors of low HDL-C disease among Kazakhs, the C-C-C-A-A-A, C-T-G-G-A-A, and T-T-C-G-A-A haplotypes may serve as protective factor of low HDL-C disease among Kazakhs.

A complex phenotype in a child with familial HDL deficiency due to a novel frameshift mutation in APOA1 gene (apoA-IGuastalla).

BACKGROUND: We describe a kindred with high-density lipoprotein (HDL) deficiency due to APOA1 gene mutation in which comorbidities affected the phenotypic expression of the disorder. METHODS: An overweight boy with hypertriglyceridemia (HTG) and HDL deficiency (HDL cholesterol 0.39 mmol/L, apoA-I 40 mg/dL) was investigated. We sequenced the candidate genes for HTG (LPL, APOC2, APOA5, GPIHBP1, LMF1) and HDL deficiency (LCAT, ABCA1 and APOA1), analyzed HDL subpopulations, measured cholesterol efflux capacity (CEC) of sera and constructed a model of the mutant apoA-I. RESULTS: No mutations in HTG-related genes, ABCA1 and LCAT were found. APOA1 sequence showed that the proband, his mother and maternal grandfather were heterozygous of a novel frameshift mutation (c.546_547delGC), which generated a truncated protein (p.[L159Afs*20]) containing 177 amino acids with an abnormal C-terminal tail of 19 amino acids. Trace amounts of this protein were detectable in plasma. Mutation carriers had reduced levels of LpA-I, preß-HDL and large HDL and no detectable HDL-2 in their plasma; their sera had a reduced CEC specifically the ABCA1-mediated CEC. Metabolic syndrome in the proband explains the extremely low HDL cholesterol level (0.31 mmol/L), which was half of that found in the other carriers. The proband's mother and grandfather, both presenting low plasma low-density lipoprotein cholesterol, were carriers of the ß-thalassemic trait, a condition known to be associated with a reduced low-density lipoprotein cholesterol and a reduced prevalence of cardiovascular disease. This trait might have delayed the development of atherosclerosis related to HDL deficiency. CONCLUSIONS: In these heterozygotes for apoA-I truncation, the metabolic syndrome has deleterious effect on HDL system, whereas ß-thalassemia trait may delay the onset of cardiovascular disease.

Defective functionality of HDL particles in familial apoA-I deficiency: relevance of alterations in HDL lipidome and proteome.

To evaluate functional and compositional properties of HDL in subjects from a kindred of genetic apoA-I deficiency, two homozygotes and six heterozygotes, with a nonsense mutation at APOA1 codon -2, Q[-2]X, were recruited together with age- and sex-matched healthy controls (n = 11). Homozygotes displayed undetectable plasma levels of apoA-I and reduced levels of HDL-cholesterol (HDL-C) and apoC-III (5.4% and 42.6% of controls, respectively). Heterozygotes displayed low HDL-C (21 ± 9 mg/dl), low apoA-I (79 ± 24 mg/dl), normal LDL-cholesterol (132 ± 25 mg/dl), and elevated TG (130 ± 45 mg/dl) levels. Cholesterol efflux capacity of ultracentrifugally isolated HDL subpopulations was reduced (up to -25%, P < 0.01, on a glycerophospholipid [GP] basis) in heterozygotes versus controls. Small, dense HDL3 and total HDL from heterozygotes exhibited diminished antioxidative activity (up to -48%, P < 0.001 on a total mass basis) versus controls. HDL subpopulations from both homozygotes and heterozygotes displayed altered chemical composition, with depletion in apoA-I, GP, and cholesteryl ester; enrichment in apoA-II, free cholesterol, and TG; and altered phosphosphingolipidome. The defective atheroprotective activities of HDL were correlated with altered lipid and apo composition. These data reveal that atheroprotective activities of HDL particles are impaired in homozygous and heterozygous apoA-I deficiency and are intimately related to marked alterations in protein and lipid composition.

Treatment of low HDL-C subjects with the CETP modulator dalcetrapib increases plasma campesterol only in those without ABCA1 and/or ApoA1 mutations.

We investigated the effect of dalcetrapib treatment on phytosterol levels in patients with familial combined hyperlipidemia (FCH) or familial hypoalphalipoproteinemia (FHA) due to mutations in apolipoprotein A1 (ApoA1) or ATP-binding cassette transporter A1 (ABCA1). Patients (n = 40) with FCH or FHA received dalcetrapib 600 mg or placebo in this 4-week, double-blind, crossover study. Lipids, apolipoproteins, cholesteryl ester transfer protein (CETP) activity and mass, and phytosterols were assessed. Dalcetrapib increased high-density lipoprotein cholesterol (HDL-C) and ApoA1 levels to a similar extent in FHA (+22.8, +13.9%) and FCH (+18.4, +12.1%), both p < 0.001 vs. placebo. Changes in CETP activity and mass were comparable for FHA (-31.5, +120.9%) and FCH (-26.6, +111.9%), both p < 0.0001 vs. placebo. Campesterol and lathosterol were unchanged in FHA (+3.8, +3.0%), but only campesterol was markedly increased in FCH (+25.0%, p < 0.0001 vs. placebo). Campesterol increased with dalcetrapib treatment in FCH but not in FHA, despite comparable HDL-C and ApoA1 increases, suggesting that ApoA1 and/or ABCA1 is essential for HDL lipidation by enterocytes in humans.

High-density lipoprotein metabolism, composition, function, and deficiency.

PURPOSE OF REVIEW: To examine the recent advances in our knowledge of HDL metabolism, composition, function, and coronary heart disease (CHD), as well as marked HDL deficiency states because of mutations in the apolipoprotein (apo) A-I, ATP-binding cassette transfer protein A1 and lecithin cholesterol acyltransferase (LCAT) gene loci. RECENT FINDINGS: It has been documented that apoA-I, myeloperoxidase and paraoxonase 1 (PON1) form a complex in HDL that is critical for HDL binding and function. Myeloperoxidase has a negative impact on HDL function, whereas PON1 has a beneficial effect. Patients who lack apoA-I develop markedly premature CHD. Patients who lack ATP-binding cassette transfer protein A1 transporter function have only very small discoidal preß-1 HDL, and develop hepatosplenomegaly, intermittent neuropathy and premature CHD, although significant heterogeneity for these disorders has been reported. Patients with LCAT deficiency have abnormal small discoidal LDLs and HDL particles, and develop kidney failure. Enzyme replacement therapy is being developed for the latter disorder. SUMMARY: Recent data indicates that proteins other than apoA-I and apoA-II such as MPO and PON1 have important effects on HDL function. There has been considerable recent progress made in our understanding of HDL protein content and function.

Ultrasound-directed, site-specific gene delivery.

With the implementation of gene therapy looming in the near term, an effective delivery system using noninvasive, nonviral-mediated methods appears as an attractive option. This novel platform technology uses gas-filled, ultrasound-directed acoustic microspheres for both diagnostic imaging and therapy and yet may provide a key component for future success in the pursuit of single-gene replacement therapy.

Mutation mapping of apolipoprotein A-I structure assisted with the putative cholesterol recognition regions.

Twenty-nine from 52 missense mutations in apoA-I gene are predicted to be deleterious by both SIFT and PolyPhen-2 algorithms. Among those, eight mutations with a prominent change in structure stability as modeled by the SDM tool for both lipid-free (Mei and Atkinson (2011) PDB ID: 3R2P) and HDL-bound (Wu et al. (2009) PDB ID: 3K2S) apoA-I, are referred as structural. The remaining mutations with a preferential location in a long intrinsically disordered region, predicted by the SPINE-D and DNdisorder tools, may influence the functional sites. Among structural mutations, five amyloidosis-only-related mutations, significant in a lipid-free structure, are located in 1-90 region. Six amyloidosis- and hypoalphalipoproteinemia-associated mutations, differently significant in two chains of lipid-bound apoA-I, are distributed among the N-domain. Six cholesterol recognition putative motifs (5 CRAC/1 CCM) in apoA-I structure are suggested to interact with cholesterol. Among those, the K40-W50 partially conserved CCM sequence with a putative recognition feature, predicted by the MoRF tool, may underlie cholesterol binding to lipid-free apoA-I, the binding triggering the disorder-to-order transition within MoRF. Thus, the impairment of helix formation and accelerated protein aggregation may underlie the amyloidogenic effect of W50R substitution. Also, D102H substitution in conserved CRAC2 V97-K106 sequence may be harmful in reverse cholesterol transport. With PDBe Motifs and Sites algorithm, cholesterol is a ligand for L101, F104 and W108 residues in HDL-bound apoA-I. The influence of specific mutation on apoA-I structure and mutated apolipoprotein switch between different pathologies is suggested to depend on the surrounding phase properties.

Genomic study in Mexicans identifies a new locus for triglycerides and refines European lipid loci.

BACKGROUND: The Mexican population and others with Amerindian heritage exhibit a substantial predisposition to dyslipidemias and coronary heart disease. Yet, these populations remain underinvestigated by genomic studies, and to date, no genome-wide association (GWA) studies have been reported for lipids in these rapidly expanding populations. METHODS AND FINDINGS: We performed a two-stage GWA study for hypertriglyceridemia and low high-density lipoprotein cholesterol (HDL-C) in Mexicans (n=4361), and identified a novel Mexican-specific genome-wide significant locus for serum triglycerides (TGs) near the Niemann-Pick type C1 protein gene (p=2.43×10(-08)). Furthermore, three European loci for TGs (APOA5, GCKR and LPL), and four loci for HDL-C (ABCA1, CETP, LIPC and LOC55908) reached genome-wide significance in Mexicans. We used cross-ethnic mapping to narrow three European TG GWA loci, APOA5, MLXIPL, and CILP2 that were wide and contained multiple candidate variants in the European scan. At the APOA5 locus, this reduced the most likely susceptibility variants to one, rs964184. Importantly, our functional analysis demonstrated a direct link between rs964184 and postprandial serum apoAV protein levels, supporting rs964184 as the causative variant underlying the European and Mexican GWA signal. Overall, 52 of the 100 reported associations from European lipid GWA meta-analysis generalised to Mexicans. However, in 82 of the 100 European GWA loci, a different variant other than the European lead/best-proxy variant had the strongest regional evidence of association in Mexicans. CONCLUSIONS: This first Mexican GWA study of lipids identified a novel GWA locus for high TG levels; used the interpopulation heterogeneity to significantly restrict three previously known European GWA signals, and surveyed whether the European lipid GWA SNPs extend to the Mexican population.

HDL deficiency due to a new insertion mutation (ApoA-INashua) and review of the literature.

A 61-year-old white man of European ancestry with significant coronary heart disease since age 42 years and marked high-density lipoprotein (HDL) deficiency (HDL cholesterol 1 mg/dL) was evaluated. His fasting low-density lipoprotein cholesterol level was 42 mg/dL, and his triglycerides were 417 mg/dL on therapy with rosuvastatin 40 mg/day, ezetimibe 10 mg/day, fenofibrate 145 mg/day, and extended-release niacin 2 g/day. Further analysis of his plasma revealed an apolipoprotein (apo) A-I level of 23.5 mg/dL (approximately 20% of normal), and the absence of small alpha-4 HDL, medium alpha-3 HDL, and very large alpha-1 HDL, with only very small pre-beta-1 HDL and large alpha-2 HDL being present. APOA-I gene sequencing revealed a novel heterozygous in-frame insertion mutation with duplication of nucleotides 1535 through 1552 inserted at position 1553, causing a new amino acid glycine at codon 157 and a duplication of amino acids alanine, arginine, alanine, histidine, and leucine at codons 158-162. This novel apoA-I mutation results in the formation of apoA-I that appears to have abnormal lipid binding properties, resulting in impaired reverse cholesterol transport, probable enhanced clearance, and premature coronary heart disease.

Novel mutations of ABCA1 transporter in patients with Tangier disease and familial HDL deficiency.

The objective of the study was the characterization of ABCA1 gene mutations in 10 patients with extremely low HDL-cholesterol. Five patients (aged 6 months to 76 years) presented with splenomegaly and thrombocytopenia suggesting the diagnosis of Tangier disease (TD). Three of them were homozygous for novel mutations either in intron (c.4465-34A>G) or in exons (c.4376delT and c.5449C>T), predicted to encode truncated proteins. One patient was compound heterozygous for a nucleotide insertion (c.1758_1759insG), resulting in a truncated protein and for a nucleotide substitution c.4799A>G, resulting in a missense mutation (p.H1600R). The last TD patient, found to be heterozygous for a known mutation (p.D1009Y), had a complete defect in ABCA1-mediated cholesterol efflux in fibroblasts, suggesting the presence of a second undetected mutant allele. Among the other patients, four were asymptomatic, but one, with multiple risk factors, had severe peripheral artery disease. Three of these patients were heterozygous for known mutations (p.R130K+p.N1800H, p.R1068C, p.N1800H), while two were carriers of novel mutations (c.1195-27G>A and c.396_397insA), predicted to encode truncated proteins. The pathogenic effect of the two intronic mutations (c. 1195-27G>A and c.4465-34A>G) was demonstrated by the analysis of the transcripts of splicing reporter mutant minigenes expressed in COS-1 cells. Both mutations activated an intronic acceptor splice site which resulted in a partial intron retention in mature mRNA with the production of truncated proteins. This study confirms the allelic heterogeneity of TD and suggests that the diagnosis of TD must be considered in patients with an unexplained splenomegaly, associated with thrombocytopenia and hypocholesterolemia.

Genetic lecithin:cholesterol acyltransferase deficiency and cardiovascular disease.

The lecithin:cholesterol acyltransferase (LCAT) enzyme is responsible for the synthesis of cholesteryl esters in human plasma and plays a critical role in high density lipoprotein (HDL) metabolism. Genetic LCAT deficiency is a rare metabolic disorder characterized by low HDL cholesterol levels. This paper reviews the genetic and biochemical features of LCAT deficiency, highlighting the absence of enhanced preclinical atherosclerosis in carriers, despite the remarkably low HDL cholesterol.